Bringing hundreds of years’ experience together as a strategy for applying open- source, standards, and specs to space travel—an endeavor with challenges to spare.

VME has been around for 35+ years and owns a venerable place in test and measurement, military, aerospace, research, and industrial applications. However, engineers currently managing systems with VME backplanes have been talking about VPX for a while, with the focus of interest in migrating legacy VME systems to something with more capability. In its prime, VME was quite good at making possible the use of the latest technology in the same chassis as the original technology. VPX is trying to emulate that tolerance; however, success is a good deal more difficult due to ever faster signaling speeds in modern backplanes.

Figure 1: Eastern Europe in a night space flight. (Source: NASA)

VPX, a system-level standard, includes all the market segments that VME has served and then some. High-performance computing, scalability, and flexibility are gaining new definition, sparked by technology’s stretching standards to new goals. Future-proofing and standards that encourage open source architectures are recent goals. VPX not only includes applications like real-time hardware-in-the-loop (HITL) testing and data acquisition, but also Electronic Warfare (EW), RADAR, Signals Intelligence (SIGINT), Communications Intelligence (COMINT), and a host of other technologies that reside within high-performance computing and demanding aerospace/mil markets.

Work on the VPX (VITA 46) specification began in 2004 and was ratified in 2007. OpenVPX (VITA 65) was ratified in 2009 and is meant to improve interoperability between modules at the system-level. OpenVPX can be thought of as the architectural framework for the VPX standard. It specifies a set of system profiles. The OpenVPX Systems Specification defines an architecture framework that manages and constrains module and backplane designs, including defining pinouts, and sets interoperability points within VPX while maintaining full compliance with VPX.

OpenVPX is an open standard. The term “open standard,” ironically, has no standard definition. For VITA “open standard” means that OpenVPX is not proprietary, is collaboratively developed with little restriction by a VITA working group, and is “owned” by the VITA collective body. Anyone that wants to participate in a working group at VITA need only be a VITA member in good standing. VPX standards have focused on the board level, and OpenVPX focuses on the framework surrounding all that is defined within the VPX standard. OpenVPX is fully compliant with VPX.

An industry that has been a government monopoly until recently is space travel—a Space, Weight, and Power (SWaP) constrained endeavor, to which extreme high-performance computing adds still more challenges. However, commercial space flight interests such as Virgin Galactic and SpaceX may very well be using PXI and CompactPCIe (cPCIe), if job requirements for engineers are any indication (see the career section of the companies’ websites.) PXI is a PC-based modular instrumentation architecture defined by the PXI Standard and maintained by the PXI Systems Alliance. (PXI stands for PCI eXtensions for Instrumentation.)

Figure 3: A 2016 SpaceX rocket launch. (Source: SpaceX.com)

Have commercial space-flight companies entertained VPX at any point? Or do PXI and cPCIe reflect a comfort zone for a greater population of engineers? PCI was originally created for personal computers. Perhaps the largest detriment within CompactPCI Express systems is that they are limited to the PCIe serial interface. Perhaps at the outset, commercial flight outfits lacked a VPX standard that extends to space. VPX was designed with modularity and robustness as a forethought and has garnered added-value from products like the MultiGig RT2 connector by TE Connectivity, which has transfer rates of up to 6.25 Gbps and documented crosstalk at less than 3%. VPX offers both the standard 19-inch (6U) and compact single (3U) form factor. VPX offers a high-throughput interconnection system in a compact frame with the scalability and flexibility to benefit future requirements.

“Future Proof” in the Bullseye

However, VPX alone does not specifically accommodate space flight requirements. Enter SpaceVPX. SpaceVPX (VITA 78) is an enhanced version of ANSI/VITA OpenVPX. A government-industry collaboration has set forth a Next Generation Space Interconnect Standard (NGSIS) “to define a set of standards for interconnects between space system components with the goal of cost-effectively removing bandwidth as a constraint for future space systems [1] .” NGSIS has chosen the VITA 65 OpenVPX standard using RapidIO (RIO) as the protocol. OpenVPX features interoperability and robustness for the harsh space environment. These features combine with affordability due to leveraging existing modern standards, an approach that could enable Commercial Off-the-Shelf (COTS) module use, and flexibility. The NGSIS goal noted above, “cost effectively removing bandwidth as a constraint for future space systems,” could mean that SpaceVPX is aiming for “future-proof.” SpaceVPX seeks to balance an acceptable level of fault tolerance with a reasonable level of compatibility with existing VPX components, including pin connector assignments. It creates a space version of profiles for slots, modules, and backplanes. Further space-specific extensions are being worked through the VITA 78, or SpaceVPX working group, under the VITA Standards Organization. Interoperability is key, and RapidIO is an asset of interoperability that SpaceVPX inherits from VPX.

A Living Standard

VPX is a good place for SpaceVPX to start. “Interoperability is a better solution than a proprietary solution that has limited options and supporters. Both are still complex systems that take a fair amount of skill and knowledge to build systems around them, but they have large communities of suppliers and users that work together to build systems,” states Jerry Gipper, Executive Director of VITA. “OpenVPX (VITA 65) helps with interoperability by defining how that multitude of options should work together to ensure that all levels of a system work properly. OpenVPX is a living standard: As new requirements emerge, the community works together to define interoperable profiles that make it easier to develop complex systems.”

SpaceVPX includes main elements from VITA 46 VPX and ANSI/VITA 65 OpenVPX. These existing standards are in alignment with many requirements for space travel, including such features as full redundancy of modules, which hits check marks for meeting fault tolerance requirements for space systems. Flexibility is part of the working group’s goals within the guideline of OpenVPX, which was created in part to narrow the profusion of choices so that the benefits of open standards could be realized. For example, SpaceVPX fully supports a peer-to-peer mesh network instead of switches. Nevertheless, combining both mesh and switching topologies can be easily accommodated. The newly evolving standard accommodates a variety of compatible connectors, including those compliant to ANSI/VITA 60 and 63. In turn, ANSI/VITA 48.2[3] is the basis for allowable mechanical extensions in the new standard. ANSI/VITA 62 defines a standardized power module.

And to eliminate the limitations of copper, SpaceVPX has a goal to apply ANSI/VITA 66 and 67 to replace electrical segments of the connector with RF or optical. One of the main benefits of open standards is the benefit of interoperability. Thus the challenges of interface management are met with a well-defined common interface “that allows for conformance verification without a complete system.”

Figure 4: An example of the OpenVPX system architecture. Some use multiple planes to isolate traffic. Source: “Architectures for High-Performance Embedded Computing, Cooper (Mercury Computer Systems) and Littlefield (Curtiss-Wright Controls).

SpaceVPX features the RapidIO switched fabric protocol, which is “an efficient, high-performance packet switching architecture to provide an interconnect capability suitable for chip-to-chip and board-to-board communications[2]. ” RIO has scalable data rates in each lane, up to a maximum of 6.25 Gbps. RIO allows one to aggregate lanes into channels with capacities of 40 Gbps (8 lanes) to 80 Gbps (16 lanes) and has a roadmap to achieve higher rates later.

Virgin Galactic, SpaceX, and any other entities associated with space travel are free to participate in the SpaceVPX working group and help shape the future of fast, reliable and open standards for space travel, according to Patrick Collier, Space Vehicles Directorate at the Kirtland Air Force Research Laboratory. “SpaceVPX is an open standard. There are already enough challenges to space travel, including budget constraints. Open source, open standards, and specs have proven to not only reduce overall cost in the long run but increase reliability and even security as hundreds of years of experience are combined in one working group. Collaborating on this backplane standard involves sharing of best practices.” Space flight endeavors now have a faster, lower latency alternative to existing backplane solutions: SpaceVPX (VITA 78).

When asked, Collier agreed that commercial space flight interests such as Arianespace, SpaceX, and Virgin Galactic would be welcome in the working group and effort. Arianespace launched 11 flights in 2016. SpaceX launched 8 flights in 2016 and boasts a launch manifest that includes “space-station resupply missions, commercial satellite launch missions, and US government science and national security missions.” Virgin Galactic, “the world’s first commercial space line,” has a different mission. Virgin has taken roughly 700 deposits for spaceflight tourism and launch systems for small satellites. Although commercial space ventures are competitive, there is room for open systems because openness as a business model is proven to reduce complexity, cost, and increase safety by combining the experience of hundreds of years of experience of all involved in the working group. Open standards like SpaceVPX also have potential to commoditize modules for space-rated systems, reducing non-recurring engineering (NRE) charges.

No Wheel Re-Invention Here

VNX VITA 74 is another VITA specification suited for small form-factor rugged requirements, including space exploration, and is especially suited for smaller CubeSats, with a 19mm size VNX module fitting into 4 slots and a 12.5mm module for the fifth slot. Also referred to as “NanoX,” VNX VITA 74 is based on VPX (VITA 46) and includes two serial fabrics: Ethernet and PCI Express. To maintain simplicity, just one processor root node is specified. VITA 57 (FMC) specifies the connectors used in NanoX (VNX VITA 74). Alternatively, less compute-intense designs that do not require fully loaded VPX can be ported down to VNX, since VNX is so similar to VPX technology, barring form factor and of course, more compact modules. VNX offers a more compact, lower-cost option to an underutilized VPX solution.

NGSIS has a goal to create standards that provide enough flexibility so users can implement several different system configurations and maintain interoperability, all on the bedrock of a chassis standard intended from the outset to meet the hazards of outer space. “SpaceVPX has evolved from a desire to achieve low-cost solutions and from a desire to change the paradigm by which business in the Space Industry is conducted.” The space community can only find technical and financial progress in a working group effort as sponsored by NGSIS in collaboration on SpaceVPX, with emphasis on all parties functioning as a group. Space flight and space operations are inherently inhospitable to life, costly, and stretch the limits of engineering.

Collaborative efforts that produce fruit such as SpaceVPX harness one of the major strengths of humanity: collaborative intelligence and a willingness to work together for a shared advantage. Not “re-inventing the wheel” for space-qualified communications is just smart.

Lynnette Reese is Executive Editor, Embedded Systems Engineering, and has been working in various roles as an electrical engineer for over two decades. She is interested in open source software and hardware, the maker movement, and in increasing the number of women working in STEM so she has a greater chance of talking about something other than football at the water cooler.

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